Aromatic vinyl-conjugated diene-aromatic vinyl block copolymers such as a styrene-isoprene-styrene block copolymer (SIS) and a styrene-butadiene-styrene block copolymer (SBS) are thermoplastic elastomers having characteristic properties in various aspects, and are therefore used in a variety of applications. Among thermoplastic elastomers, since aromatic vinyl-conjugated diene-aromatic vinyl block copolymers in particular are highly elastic and flexible, use of the copolymers as a material for stretchable films used in hygiene products such as disposable diapers and sanitary products, has become one of representative applications of aromatic vinyl-conjugated diene-aromatic vinyl block copolymers.
Since hygiene products such as disposable diapers and sanitary products are required to have following capability and fittability to the movement of wearers, stretchable films are used in various parts of these products. For example, in pull-up type diapers which are a type of disposable diapers, stretchable films are used in the opening areas around the legs, the opening area around the waist, and both hip areas. Since it is necessary that hygiene products do not move out of place even if the wearers move very actively or if the hygiene products are worn for a long time period, stretchable films that are used in such applications are required to have both a high elastic modulus and a small permanent elongation. However, regarding the conventional aromatic vinyl-conjugated diene-aromatic vinyl block copolymers, it has been inappropriate to say that a good balance is achieved between these characteristics. Therefore, investigations have been extensively carried out to improve the elastic modulus or the permanent elongation of aromatic vinyl-conjugated diene-aromatic vinyl block copolymers.
For example, Patent Literature 1 discloses that when an elastomeric polymer blend composition containing: 65 to 92 parts by weight of a specific elastomer-monovinylidene aromatic-conjugated diene block copolymer having a monovinylidene aromatic content of less than 50% by weight, and 8 to 35 parts by weight of a specific thermoplastic monovinylidene aromatic-conjugated diene block copolymer having a monovinylidene aromatic content of 50% by weight or more, is used, elastomer articles exhibiting excellent elasticity and stress relaxation characteristics are obtained.
Furthermore, Patent Literature 2 discloses that when a composition obtainable by incorporating a specific polyisoprene or the like into a specific aromatic vinyl-conjugated diene block copolymer is extrusion molded, a stretchable film which is anisotropic and excellent in flexibility, and which is suitably used as a member of hygiene products such as disposable diapers and sanitary products, is obtained.
However, even the technologies described in these Literatures are still unsatisfactory from the viewpoint of achieving a high-level balance between a high elastic modulus and a small permanent elongation, and further improvements have been desired.
Furthermore, Patent Literature 3 describes that when a blend of an aromatic vinyl-conjugated diene block copolymer with polyolefin is produced into a film by extrusion molding, the film exhibits an elastic property that is different in the longitudinal direction from that of the horizontal direction, and thus, is suitably used as a film dedicated for a specific use where such anisotropic is desired. However, even the technology described in Patent Literature 3 is still unsatisfactory from the viewpoint of achieving a high-level balance between a high elastic modulus and a small permanent elongation.
Incidentally, when a stretchable film is used in hygiene products such as disposable diapers or sanitary products, great importance is attached to texture or flexibility. Therefore, for example, a stretchable laminate which is formed by laminating a non-woven fabric on at least one surface of a stretchable film, such as disclosed in Patent Literature 4, is used as a stretchable member in many cases. In such a laminate, an adhesive force that is so strong that the non-woven fabric and the stretchable film would not undergo peeling during the production process or during the use of the hygiene product, is required. It is also desired that such a laminate be produced with satisfactory productivity.